Oberon processing demo module

gistfile1.txt

MODULE Tree;
  IMPORT PageInit, P := Processing;

  VAR
    theta : REAL;

  PROCEDURE Branch(h : REAL);
  BEGIN
    h := 0.66*h;

    IF h > 2.0 THEN
      P.PushMatrix;
      P.Rotate(theta);
      P.Line(0.0, 0.0, 0.0, -h);
      P.Translate(0.0, -h);
      Branch(h);
      P.PopMatrix;

      P.PushMatrix;
      P.Rotate(-theta);
      P.Line(0.0, 0.0, 0.0, -h);
      P.Translate(0.0, -h);
      Branch(h);
      P.PopMatrix;      
    END
  END Branch;

  PROCEDURE Setup;
  BEGIN
    P.SetSize(640,360);
    P.SetBackground(0H)
  END Setup;
 
  PROCEDURE Draw;
  VAR
    a : REAL;
  BEGIN
    P.SetBackground(0H);
    P.SetFrameRate(30);
    P.Stroke(0FF00FF00H);

    a     := P.MouseX/FLT(P.Width)*90.0;
    theta := P.Radians(a);
  
    P.Translate(FLT(P.Width)/2.0, FLT(P.Height)); 
    P.Line(0.0, 0.0, 0.0, -120.0);
    P.Translate(0.0, -120.0);
    
    Branch(120.0)
  END Draw;

BEGIN
  PageInit.CreateCanvas;
  P.SetSetupProc(Setup);
  P.SetDrawProc(Draw);
  P.Start
END Tree.